B.3.1 Flashcards
(16 cards)
Alveoli
Alveoli are tiny round sacs in the lungs and they are where gas-exchange happens between the air and the blood. Surrounding the alveoli there are a network of capillaries.
For gas-exchange to happen most effectively, alveoli are adapted to have a larger surface area to volume ratio in different aspects:
- One being the thinness of alveoli, they are composed of a single layer of type I pneumocytes that are flattened for a larger SA:V ratio.
- Another the fact that one alveoli group there is a large number of alveoli making protruding spheres instead of just one sphere, this way more surface area is exposed increasing the SA:V ratio.
Lastly, in the alveoli there also are these cells called type II pneumocytes that secrete a fluid called a surfactant, its made of phospholipids that form a thin film on the surface of the alveoli to protect it. It protects it by reducing surface tension which prevents the alveoli walls to stick together when they compress together during expiration.
Diffusion
Diffusion is a process for gas exchange in which gases move across a membrane from a high concentration to a low concentration. This process is slow as the molecules move randomly, so for the gas exchange to be maximised a large SA:V ratio is ideal so the distance the gases must travel is as small as possible and there is as much space for the gas exchange to happen.
Bohr shift
Increases of CO2 in the blood means that CO2 dissolves into the plasma which decreases the pH of the blood making more acidic because it bonds with hydrogen in water making it form carbonic acid, this will make the haemoglobin loose affinity for oxygen shifting the oxygen disassociation curve.
Gas exchange surface
When organisms grow their volume increase at twice the speed of their surface area which reduces efficiency for gas exchange.
- To prevent this, unicellular organisms for example will increase the SA:V ratio by extending their outer surface.
- For multicellular organisms they have has to evolve specific systems for gas exchange to occur in their bodies, for example:
- internal/external gills
- Lungs
- Stomata
- Spongy mesophyll
Gas exchange surfaces have 4 properties
- Moisture
- Thinness
- Large surface area
- Permeability
Concentration gradients
For gas exchange to happen there needs to be a concentration gradient of gases moving from a high concentration to a low concentration, but for the gases to keep being exchanges the concentration gradient must be maintained. For this to happen the gases need to be transported away after gas exchange so that the area receiving gases keeps having a low concentration.
- unicellular organisms continuously use oxygen so the concentration is always lower in the cell.
- At tissue level the blood maintains the concentration gradient by constantly moving blood through the capillaries, that way there is always a concentration gradient between the blood and tissues.
- At organ level the ventilation system actively moves air (in the lungs) or water (in the gills) over the Respiratory surface.
Leaf tissue
The leaf tissue consists of (in order):
- A waxy cuticle that covers it outside of the leaf and prevents water loss.
- The upper epidermis where there is a layer of cells that protects the inner part of tissue and secretes the waxy cuticle to the outside of the tissue.
- The palisade mesophyll is a layer of tightly packed palisade cells that contain many chloroplasts to maximize photosynthesis.
- The vascular bundle is a bundle found in the spongy mesophyll that consists of xylem and phloem, xylem is on the top and transports water and nutrients from the root to the leaf, while phloem is at the bottom and contains sugar and nutrients and goes from the leaf to the roots.
- The lower epidermis is the same as the upper but just under, it contains the guard cells and stomata.
- The guard cells are cells in charge of opening and closing the stomata depending on the transpiration rate and are responsible for gas exchange.
- The stomata are fenestration that are in charge of gas-exchange and for water loss.
Oxygen dissociation curve
The oxygen dissociation curve is a sigmoid curve that shows the correlation between the partial pressure of and the percentage of saturation with oxygen in haemoglobin. The reason for its curved shape instead of a straight line is because of the conformational change in haemoglobin that causes a change of affinity with oxygen. Once one oxygen binds to a haem group in haemoglobin there is a conformational change that causes haemoglobin to have a higher affinity to oxygen, so then after the one, 3 other oxygen molecules bond with the remaining binding cites much quicker causing the curve instead of the straight line, then once they have bonded it becomes stable and constant.
Transpiration
Transpiration is the process of water evaporating from the leaf tissues to the outside of it, this leads to water molecules pulling each other up with cohesion as they leave the tissue (from the root to the leaves through the stem). Transpiration occurring depends on the concentration of water vapour in the air spaces in the leaf tissue compared to the outside. This is because If the outside is humid then the rate of transpiration is slower because the water vapour that is highly concentrated on the outside already keeps the surface moist for gas exchange. The opposite goes for when the outside air is dry.
Stomata
The stomata are fenestrations in the leaf tissue in its lower epidermis with the pressure of gas-exchange and water loss. They have cells next to them called guard cells that are in charge of opening and closing the stomata depending of the transpiration rate so that the plant does not loose unnecessary water. When there is low water vapour pressure (when the transpiration rate is low) the guard cells close the stomata and the opposite happens when there is high water vapour pressure. The stomata also close during the night since there is no sunlight for photosynthesis therefore staying open would cause unnecessary water loss.
To calculate stomatal density the formula is as follows:
Stomatal density (mm^-2)= mean number of stomata/area of field of view (mm^2)
fetal and adult Haemoglobin
Foetal haemoglobin is composed differently than adult haemoglobin because instead of 2 alpha and 2 beta polypeptide chains, foetal haemoglobin have 2 alpha and 2 gamma polypeptide chains. The main change this causes is that the haemoglobin in foetuses has a higher affinity to oxygen since it has to travel all the way from the mom’s system to the foetus’.
Affinity
Affinity is the bond molecules have between each other. When they have a high affinity it means that they have a strong attraction to each other and become tightly bound together. But when molecules have a low affinity it meas that they are loosely tied together and break apart easily.
Cooperative binding of oxygen
The cooperative binding of oxygen is in haemoglobin where the iron in the haem group has a conformational change when bonding to its first oxygen molecule causing the affinity for oxygen molecules to increase, this way the 3 remaining binding cites for oxygen are taken much faster than the first one. The same happens for the opposite of one oxygen leaving, the affinity to oxygen lowers and the other 3 oxygen molecules leave quicker than the first one.
This can be seen in the oxygen dissociation curve creating the sigmoid curve.
Pressure and volume in ventilation
As the volume of gas decreases its pressure increases and visa versa. This explains how the changes in pressure in the lungs cause the changes to the volume of the chest cavity during inspiration and expiration. When the chest cavity volume is smaller, the pressure is greater, and when the chest cavity volume is larger the pressure is lower.
This helps air be pushed out in expiration when the pressure is greater in the lungs because air will move from higher pressure to lower pressure, the same for the opposite.
The respiratory system
The respiratory system is a network of tissues and organs that work together to facilitate gas exchange between the body and the environment.
It is composed of
- The upper respiratory track: the mouth, the nose, the pharynx, and the larynx. This part is in charge of warming up and moistening the air brought into the body.
- The lungs: spongy organs where gases O2 and CO2 are exchanged between the blood and the air.
- The muscles: The diaphragm is a partition between the chest and the abdominal cavity while the intercostals are muscles between the rib bones that move opposite to the diaphragm when contracting.
- Lower respiratory tract: this is the trachea, bronchi, and bronchioles, a series of branching tubes that transport air in and out of the lungs
- Alveoli: the tiny sacs in the lungs where gas exchange happens in the lungs between the air and the blood in the capillary beds.
Measurements of lung volumes
To show lung volumes and breathing frequency over time a spirometer is used and when the information taken is graphed it is in a Spirograph. In a spirograph there are different factors put in:
- The ventilation rate, this is the number of inspirations and expiration cycles taken per minute
- Tidal volume, is the volume of air moved in and out of the lungs during a normal breath cycle
- Vital capacity, is the maximum amount of air that a person can exhale from their lungs after taking in the maximum air they can inhale
- Inspiratory reserve volume is the amount of air that can be inhaled forcefully after a normal breath
- Expiratory reserve volume is the amount of air that can be exhaled forcefully after a normal breath
Ventilation cycle
In inspiration the diaphragm contracts and moves down pushing the abdomen down, the abdomen is relaxed, the internal intercostal is also relaxed while the external intercostal is contracting pulling the ribcage up and out
In expiration the diagram is relaxed upwards, the abdomen contracts and pushes the abdominal organs and diagram upwards, the external intercostal is relaxed, and the internal intercostal is contracting pulling the ribcage in and down.
